The present invention relates to a roof paver element and a roof paver system including a plurality of interconnected roof paver elements for covering roofs and, especially, for covering the membranes of single-ply roofing systems.
For most types of low-slope roofs, roof ballast is used to hold down the roofing membrane against the roof deck when wind conditions may create negative pressures tending to lift the membranes. The ballast also protects the membranes from ultraviolet radiation and puncture or impact damage by maintenance crews and wind-blown objects. The standard form for roof ballast has traditionally been a smooth, round "river wash" type of gravel which is spread uniformly to produce a minimum of 10 lb/sf (237 kg/m.sup.2) load on the membrane. However, the use of gravel as roof ballast has been revised in recent years in light of the development of new single-ply roofing systems and the extensive damage caused to buildings near gravel ballast roofs as the result of flying gravel in hurricane type conditions. New single-ply roofing membranes, as opposed to the conventional multi-ply "built up" roofing systems, do not use hot bitumen for holding the membranes in place, and in some cases, the single-ply membranes are laid loosely on the roof deck without fasteners other than at the perimeter, which means that heavier than usual ballast is desirable to keep the membrane down. In addition, because the gravel ballast does not adhere to the single-ply membranes as it adhered to the bitumen in the asphalt-based systems, there is a greater potential hazard of gravel flying under extreme wind conditions.
In order to overcome the drawbacks of gravel ballast, flat concrete paver elements and systems have been developed which provide adequate ballast to hold down the roof membrane and protect it from ultraviolet radiation and impact damage, but each suffers from at least one of several disadvantages. Some of the prior art roof paver elements require for their manufacture special concrete molding equipment, drying racks and handling equipment, even though they are produced by manufacturers already having conventional equipment of the same types for producing standard concrete blocks. This is due to the fact that the designs of the known paver elements require the elements to have non-standard dimensions to provide roof drainage or for other purposes, and even with such special dimensions, the provision for roof drainage is not always adequate and/or permits drainage in only one direction. Roof paver elements have flat upper surfaces which allow air to flow uninterrupted across the elements at high speeds, producing negative pressures which can lift and displace the elements. In addition, known roof paver systems do not provide a convenient arrangement for aligning and anchoring the paver elements in courses around the perimeter of the roof or a system for preventing the paver elements from sliding when they are installed in roofs having slopes higher than 1 inch per foot.